The testnet is already online since a few weeks now. But according to the segwit2x timeline this step should come tomorrow if they are still on track:

July 14 - Agreement Participants Install and Test Milestone

For the august 1th date user support for segwit2x does not matter at all. If the miners that agreed to run this software stick to it, they will start signaling bit4 on 21th July, when they reach 80% hashrate it will orphan non segwit blocks (kinda like bip148 but with miner support) and at the same time signal bit1 to lock in segwit which by then if that works has enough hashrate to overcome the 95% threshold to activate it. No user support at all needed for this.

Only the 2x part of segwit2x will need user adoption, but that comes 3 months after segwit has activated (next round of drama, long on popcorn)